New rules are needed to make sure all European fishing vessels fishing outside of EU waters operate in a sustainable way, campaigners urged on Wednesday.

The current reform of the common fisheries policy, which governs the EU fleet, must make sure that vessels exploiting fish stocks as far away as the Indian Ocean and the southern Atlantic conform to the same standards as in Europe's waters.

WWF-UK made the demand as it published a new study showing that commercial fishing fleets globally are expanding their range and fishing more intensively.

The study identified that the area heavily affected by fishing had increased tenfold since the 1950s, to around 100m square kilometres (38 million square miles) - one-third of the world's ocean surface.

More than 700 EU-flagged fishing vessels now exploit fisheries outside of Europe, including nine UK ships which fish in the Indian Ocean, in the waters of Mauritania, the Falkland Islands, Morocco and in the north-west Atlantic.

Fishing in foreign waters is led by Spain, whose 424 vessels make up 59% of the EU fleet operating in other countries' "exclusive economic zones" or on the high seas.

The conservation group said improved technology and subsidies made the EU fleet more mobile than most global fishing outfits, enabling their vessels to travel to the further corners of the world to fish and exploit new fishing areas.

The negotiation of "access agreements" with developing countries, particularly African nations such as Madagascar and Mozambique who have deals with UK vessels to fish in their Indian Ocean waters, has also allowed EU vessels access to new fisheries.

The "re-flagging" of EU vessels to allow them to evade European fishing rules in other countries' waters and fish on the high seas, outside of managed areas and individual nations' waters, made it hard to monitor their activities.

Giles Bartlett, fisheries policy officer at WWF-UK, said: "It may surprise many people to learn that a number of UK-registered boats, along with hundreds of others from across Europe, are operating as far away as the Indian Ocean and south Atlantic to catch fish.

"With many of Europe's fish stocks now depleted, improved technology along with subsidies have encouraged a growing number of EU vessels to exploit fishing opportunities across the world.

"We have a unique opportunity to fix the broken common fisheries policy, which has allowed many unsustainable practices to flourish.

"It is vital any reform guarantees vessels that fish abroad follow the same rules and respect the same sustainability principles as those operating within EU waters."

He called on the UK government to make sure not only the British fleet, but all EU vessels in foreign waters, adopt sustainable practices.

And he warned that if Europe did not take a lead on global fisheries management, it would further contribute to the crisis in the world's oceans - where four-fifths of fisheries are fully exploited or overfished - and ultimately jeopardise global food security.